Heme Oxygenase Inhibits Human Airway Smooth Muscle Proliferation via a Bilirubin-dependent Modulation of ERK1/2 Phosphorylation

Abstract

The aim of this study was to investigate whether the heme oxygenase (HO) pathway could modulate proliferation of airway smooth muscle (ASM) and the mechanism(s) involved in this phenomenon. In cultured human ASM cells, 10% fetal calf serum or 50 ng/ml platelet-derived growth factor AB induced cell proliferation, extracellular and intracellular reactive oxygen species (ROS) production and ERK1/2 phosphorylation. Pharmacological HO-1 induction (by 10 microm hemin or by 20 microm cobalt-protoporphyrin) and HO inhibition (by 25 microm tin-protoporphyrin or by an antisense oligonucleotide), respectively, reduced and enhanced significantly both cell proliferation and ROS production. Neither the carbon monoxide scavenger myoglobin (5-20 microm) nor the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one could reverse ASM proliferation induced by tin-protoporphyrin, making a role of the CO-cGMP pathway in HO-modulated proliferation unlikely. By contrast, bilirubin (1 microm) and the antioxidant N-acetyl-cysteine (1 mm) significantly reduced mitogen-induced cell proliferation, ROS production, and ERK1/2 phosphorylation. Furthermore, both bilirubin and N-acetyl-cysteine and the ERK1/2 inhibitor PD98059 significantly reversed the effects of HO inhibition on ASM proliferation. These results could be relevant to ASM alterations observed in asthma because activation of the HO pathway prevented the increase in bronchial smooth muscle area induced by repeated ovalbumin challenge in immunized guinea pigs, whereas inhibition of HO had the opposite effect. In conclusion, this study provides evidence for an antiproliferative effect of the HO pathway in ASM in vitro and in vivo through a bilirubin-mediated redox modulation of phosphorylation of ERK1/2.

Essential Roles of Raf/Extracellular Signal-regulated Kinase/Mitogen-activated Protein Kinase Pathway, YY1, and Ca2+ Influx in Growth Arrest of Human Vascular Smooth Muscle Cells by Bilirubin

“…Such a scenario could explain, at least in part, the lower level of apoptosis in bilirubin-treated hVSMC. Taillé et al (23) suggested that bilirubin in airway smooth muscle cells could also modulate the phosphorylation of ERK by a redox mechanism. Furthermore, bilirubin could also modulate other cell signaling pathways that are cross-talking with the ERK/ MAPK pathway.…”

Neferine inhibits angiotensin II-stimulated proliferation in vascular smooth muscle cells through heme oxygenase-1

“…Conversely, over-expression of HO-1 by either transfection of the HO-1 gene or exogenous administration of a certain HO-1 inducer reduces excessive VSMC proliferation [25] . However, the effect of HO-1 on cell proliferation is highly variable and seems to be cell-type specific [8,[26][27][28] , raising an important question of whether the antiproliferative effect of neferine on VSMC could be mediated via HO-1 expression. To test this, the effects on both HO-1 expression and growth inhibition of neferine were determined with the same concentration of neferine used in the present study.…”

“…Oxidants, including ROS, are signals involved in the regulation of cell proliferation [40] . Results from Taille et al emphasize the concept that the antioxidant properties of the HO-bilirubin pathway are related not only to its ROS scavenging properties but also to the modulation of ROS production [27] . According to the above studies, although we have shown that HO-1 up-regulation by neferine participated in the inhibition of HUVSMC proliferation via suppression of ERK1/2 activation, we did not exclude the possibility that neferine may also induce the expression of other antiproliferative enzymes or that the effect of neferine may be achieved through the tightly regulated process of the multiple pathways that may be activated or inactivated by neferine.…”

Physiology and Pathophysiology of Heme

“…Iron can induce iron-binding as well as iron-exporting proteins, HO-1, p21, and genes that are relevant to cell growth. Bile pigments are potent antioxidants by scavenging oxidants and decreasing the activity of NADPH oxidase (12,36); bile pigments also could inhibit extracellular signal-regulated kinase activation (49). Through such combined effects, products of HO-1 may contribute to the cytoprotective effects of HO-1.…”